I think it's unknown and the lack of mention at all during previews for next week confirm that is what Sutter was going for. The placement certainly seemed like it would come from gemma. If it's not....I may stop watching.

Every review I've read on the episode said it was Abel's, and you can see it pouring out of his head before the camera pans down.

Edit: From tv.com

As her SUV swerved and tumbled off the road into a ditch (is Gemma the new Lori from The Walking Dead?), we feared the worst—no more trips to buy diapers for Jax—and it looked like we got halfway there. It was hard to tell, but Little Abel Teller became a kid-kebab, skewered by a tree branch and artistically bleeding all over his stuffed animal for maximum spirit-crushing effect, just in case we weren't already screaming our heads off. Sons of Anarchy is usually pretty transparent with its deaths, so the fact that we're not sure whether he's the show's youngest fatality is a good sign that he'll pull through and live for Tig to push him around on the swings once again.

the wicked child wrote:I still had it on the DVR so I pulled up the end...

Spoiler:

I still couldn't really see any visuals that Abel was cut, it was too damn dark... but the way they panned down and the blood started dripping... yeah, pretty sure it was his...

Spoiler:

Plus earlier in the episode they made sure to focus on Able's stuffed frog when he was sleeping. He had that thing cuddled up close to him and he wasn't letting it go. So at the end when it was on the floor and he wasn't making any noise it was like a child that has lost their security blanket but isn't crying and the blood dripping on it was IMO a sure fire sign that it was Able's blood.

the wicked child wrote:I still had it on the DVR so I pulled up the end...

Spoiler:

I still couldn't really see any visuals that Abel was cut, it was too damn dark... but the way they panned down and the blood started dripping... yeah, pretty sure it was his...

Spoiler:

Plus earlier in the episode they made sure to focus on Able's stuffed frog when he was sleeping. He had that thing cuddled up close to him and he wasn't letting it go. So at the end when it was on the floor and he wasn't making any noise it was like a child that has lost their security blanket but isn't crying and the blood dripping on it was IMO a sure fire sign that it was Able's blood.

Spoiler:

Guys, seriously, the kid had a tree branch through his abdomen. I watched it again.

the wicked child wrote:I still had it on the DVR so I pulled up the end...

Spoiler:

I still couldn't really see any visuals that Abel was cut, it was too damn dark... but the way they panned down and the blood started dripping... yeah, pretty sure it was his...

Spoiler:

Plus earlier in the episode they made sure to focus on Able's stuffed frog when he was sleeping. He had that thing cuddled up close to him and he wasn't letting it go. So at the end when it was on the floor and he wasn't making any noise it was like a child that has lost their security blanket but isn't crying and the blood dripping on it was IMO a sure fire sign that it was Able's blood.

Spoiler:

Guys, seriously, the kid had a tree branch through his abdomen. I watched it again.

Spoiler:

I thought he branch was next to him... didn't really see anything that led me to believe it was through him.

A DEFINITELY intoxicated Gemma is weaving back and forth on the road, trying mightily to stay awake. She over-corrects when she narrowly misses crashing head-on into a semi truck and smashes into a tree on the side of the road. It’s horrible. She’s unconscious, an obviously unhurt Thomas is screaming, and Abel is breathing funny. It’s probably that branch through his chest that’s causing the problem. Damn it, show, when you get babies involved I get a little upset!!!